Gear shaper cutter and method of making same



O. G. SIMMONS GEAR SHAPER CUTTER AND METHOD OF MAKING SAME Jur 1e 16,A 1931.

Filed`Feb. 15, 1930 2 Sheets-Sheet 2 mvENTop:

Patented June r16, 1931 i Y, -oLIvEn-'cg-jsm-M6Ns, orLAxEwoonomo cnrrnanimimmonor .manne lpplicatio'n-filed` February 415,` 1930.I Serial No".'1:t28,8,4 ,6.V i

-both-sides of the teeth, thefcuttin l Thisinvention relates to gear shaped cutteI'S`0f the type used in ar shapers and also :worm shaped' cutterso the type referred to in my application for method' of. 'cutting i f .worm wheels Aand the like, Serial No. 295,215,

filed July 25, 1928, and also for use, inv thread generating machines and the like .for cutting the vinvolute helicoid teeth of helical gears, -v

teeth of worm wheels, threads of worms, etc.,

the present invention relating particularly to'- the helical type of gear or Worm shaped cutter specifically referred to herein and the method 'of lforming the cutting edge-s of involute helicoid surface at the forwardends and intersecting the involute helicoid side sur faces of the cutter teeth.

In order to provide the necessary clearance for' the slide faces of the teeth of gear shaped cutters, thecutters are Ymade to taper away from their cutting ends. This taper is produced by generating the involute side faces of the teeth .to helices on the base cylinder which converge at a small angle. The y rack of the cutter by reason of the convergence of the involute faces is inclined with respect to the axis of the cutter. The cutter in generating a gear or-a worm is positioned A, with its axis in a plane parallel with the axis of the gear or wormand is reciprocated. in said plane.- 'In such position, the imaginary rack of the cutter is inclined at a small angle 'to the imaginary rack of the gear being generated and the cutter .is reciprocated in a direction at an angle to its own rack.

Y If the rack of the cutter coincided with the rack of the gear or worm being generated, the -form of the cutting edge would be unimportant since any line across the involute face of a cutter toothy would generate true involute c.

4 tooth facesfon the gear or worm Work blank.

However, with the cutter reciprocating in' a direction at an angle to its own rack, true 1nvolute surfaces will not be generated in the -work unless the cutting edge be of such form that the` surface which it describes duringits cuttingA stroke is an involute surface.

.Y The-intersection of the helicoid side faces of the cutter teeth with a plane .perpendicularv to the axis of the cutter is a true involute and fullls this requirement, but on one or hedges formed by the intersection. of side' acesv of the-teeth withca flat end facefperpendicular to the axis are too blunt for the most effective cutting action. In order to obtain sharper cutting edges for more effective cutting action, it "has heretofore been common practice to grind back the end facesl of thecutter with, the result that thecutting edge does not conform exactl to I' the involute 60 curve. In other words, e ciency of cutting action has been obtained at the expense of accuracy of contour f the surfaces generated by the cutter. While the resulting. inaccuracy is generally quite minute, it is, nevertheless, undesirable. c t

An important object of the present inven-V tion is to provide a cutter having involute helicoid teeth with cutting edges, each cutting edge being the locus of the points of intersection of an involute helicoid surface' normal to the involute helicoid side faces of the teeth of the'cutter.

It is also an important object of the present invention to provide a cutter with cutting- 5 teeth which will generate involute curves, in planes o f revolution, in helical gears, worms and the like, to a given pressure angle on each side of the teeth, when measured in a` plane of revolution.

It is a further important object of this invention to provide a cutter with teeth of a' predetermined form, adapting said cutter to generate involute curves to a given evolute x on each side' of the teeth of helical gears, 85 worms and other analogous articles of manun facture which are to be provided with teeth having helicoidal involute side surfaces. l

Thev present invention has for an important object to provide a gear sha ed cutter with 9 generated cutting edges 'o true 4involute b orm.

The present invention has for another im` portant object to provide a gear shaped,4

cutter with generated cutting edges of true helicoidal involute form. c. The present' invention has for a further important object to provide a helical gear p shaped cutter with cutting edges of true inim volute helicoid form.

The present invention has for a further object to provide a cutter which has superior cutting action and which may be used for relatively long periods without re-sharpen further object is to provide a cutter having teeth of helical form in which cutting edges of identical form are provided on opposite edges of each tooth and in which both o cutting edges of each tooth are formed by the intersection of surfaces disposed at substantially the same angles to each other so that when the cutter is in use, both edges will have the same cutting action.

In my copending application Serial No. 261,813, filed March 15, 1928, I have disclosed a method of forming an acute angled cutting ed e along the normally obtuse edge of a h fcal shaped tooth by which an exceedingly cl'e approximation to an involute cutting edge may be formed. However, with cutters rovided with teeth disposed at relatively arge helix angles, it is difficult to obtain a cutting edge along the normally obtuse edge of the tooth which is of involute form and which has its faces disposed at an angle to each other corresponding to the angle between the surfaces forming the cutting edge at the opposite side of the tooth.

Furthermore, in cutters having a high helix angle, one side face of the tooth intersects the end face of the cutter at an angle which is sharper than it should be for the most effective generating action.

The present invention has for an object to obtain more accurate generating cutting action in gear Shapers, thread generating machines and the like by providing a gear' shaped cutter in which the cutting edges are true involutes formed by intersecting generated surfaces of involute form.

A further object of the present invention is to provide a helical cutter in which both cutting edges of each helical tooth are formed by involute helicoid surfaces intersecting at angles of 90 or slightly less, measured in tangent planes.

A further object is to provide a method of generating true involute cutting edges on the teeth of gear shaped cutters by generating helicoid surfaces on the end faces of the teeth along the cutting edges thereof which are in- .volute to the same base cylinder as the side faces of the cutter teeth and which intersect said side faces to form involute cutting edges.

Within the scope of the term analogous articles of manufacture it is understood that there is included such articles as have teeth with side surfaces of involute helicoidal form capable of being generated on lines of convolution on a cylindrical or conical surface, to reproduce in an article of manufacture, symmetrical involute teeth, in a plane of revolution, and also symmetrical helicoidal involute teeth in substantially the surface of revolution in the eneral direction substantially longitudinal y of the axis of the article of manufacture.

The invention further consists in the means for accomplishing the foregoing objects and other objects of the invention, which will later appear, not only in the particular form herein illustrated, but in all equivalent constructions and arrangements.

,With the above and other objects in view, the invention may be said to comprise the cutter and method of making the same, as illustrated in the accompanying drawings hereinafter described and particularly set forth in the appended claims, together with such variations and modifications thereof as willv be apparent to one skilled in the art to which the invention appertains.

Reference should be had to the accompany ing drawings forming a part of this specification, in which:

Fig. 1 is an end elevation of a cutter involving the invention,

Fig. 2 is a perspective view of the cutter.

Fig. 3 is a fragmentary end elevation on an enlarged scale showing the end face of one tooth of the cutter.

Fig. 4 is a section taken on the line indicated at 4-4 in Fig. 3.

Figs. 5, 6, 7, 8 and 9 are dia ramlnatic views showing various forms o grinding wheels in engagement with the helicoid surfaces on the end face of the cutter.

F ig. 10 is a diagrammatic view showing the relatlve positions of the grinding wheel and cutter during the generation of the internal involute helicoid surface at the normally obtuse edge of a cutter tooth.

Referring to the accompanying drawings, the cutter, indicated generally by the reference numeral 1, has the form of a helical gear, being provided with helically disposed teeth 2 which have side faces 3 and 4 which are generated involute helicoid surfaces.

The end face of the cutter is disposed in a plane at right angles to the axis of the cutter and the involute helicoid side faces 3 and 4 of each tooth intersect the end face of the tooth, one at an obtuse angle and the other at an acute angle. l When the teeth of the cutter are disposed at relatively high helix angles as shown herein, the cuttlng edges which would be formed by intersection of the side faces 3 and 4 of the teeth with flat end faces would not be suitable for eicient'cutting action since the cutting edge formed' by the intersection of the tooth faces 3 with the end faces of the teeth would be very blunt, while the cutting edges formed by the intersections of the side faces ,f

conventional, one well-known phase ofthe Y helicoid. These parallel planes areforrnedby the side face of adisc milling cutter before hardening, and vsharpened in the same manner by means of a disc grinding Wheel after hardening. The cutting edges are formed, therefore, byparallel planes intersecting the involute helicoid sides of the teeth. Thus the cutting' edges do not lie in a plane of revolution. Asa. result ofithis, troublesome errors are introduced in the teeth lof the gear generated, necessitating costly subsequent operations to rectify and eliminate the errors to make them pure involutes, in a plane of revolution, to the given base circle, on each side of the teeth. y

In another well known conventional practice in thel art, the cutter is provided with` cutting edges which are the result of intersecting the side faces of the teeth to form cutting edges by means of a plane substantially normal to the helicoidal teeth at lthe pitch circle. This practice, however, pro- (luces cutting edges the loci of points of which all lie in various planes of revolution.

In both `of the conventional, Well known practices referred to, the cutting edges are obtained by a plane intersecting the involute helicoid side teeth. Thus the advantagesof involute helicoid `teeth in Work produced by the cutters are not obtained, the conventional practices referredV to resulting in the teeth of the Work having side faces of indeterminate helicoid, epitrochoid, 'involute form.

To overcome the diiculties referred to above, I prefer to provide cuttingfedges in the plane of revolution, that is to say, in a plane perpendicular tothe axis of the cutter, by intersecting theinvolute helicoid side faces of the teeth of the cutter with their normal involute helicoid of the opposite hand, this for the reason that an involute curve is a single plane curve, and if an involute helicoid is intersected by its normal involute helicoid of the opposite hand, the locus of points of the line of intersection Will lie in a plane per-- pendicular to the axis of the base or evolute circle, namely, in a plane of revolution. The involute curve of the teeth of the cutter in the plane of revolution, therefore, is not destroyed and Will reproduce teeth in the lWork` of the desired true involute form. Thus the inherent advantages of involute gearing are obtained in helical involute gears Without it being necessary to-performnany subsequent rectifying operations on the teeth of the gears or other Worlrcut by this improved cutter.

- Helical involute gears produced by this cutter, in commercial practice, as a result of this invention, are provided with true in volute curves from the base circle to the peripheral, point of the teeth, each side being like the other and therefore symmetrical. It

curacy of the cutter maybe depended upon to A`has been found, as stated above, that theae- A' reproduce true involute helicoid" surfaces on the .teeth of the Work when the cuttingedges of the cutter are made in accordance With viding cutting edges which are theresultant locus of points of intersection of an involute helicoid by its normal involute helicoid of the opposite hand. In other Words, I produce an accurate cutter by providing normal helicoidal involute surfaces of one hand on the end face of the cutter and intersecting helicoidal involute side faces of the opposite hand of the teeth of the cutter to form the cutting edges, the cutting edges being further defined as the locus of points of intersection of the righthand involute helicoid side surface of the teeth, which extend axial# 1y of the cutter, intersecting theleftha'nd involute helicoid surface onu the end face of the cutter,'wl1ich end face is radial and extends transversely of the cutter axis in a plane of revolution thereof, and vice versa for a cutter of the opposite hand.

Freni the foregoing, therefore, itis understood that the present invention contemplates the 'use of intersecting involute helicoids of the opposite hand to establish a cutting edge,

and provides that a lefthand involute helicoid gear shaped or Worm shaped' cutter has cutting edges lying in a plane of revolution and defined as the locus of points on the lefthand involute helicoid of the cutter teeth being intersected by a righthand involute'helicoid, and, similarl but in the re.-

verse order, the teeth of a rig thand involute helicoid cutter being intersected by a lefthand involute helicoid, all of said involutes havmg the same base orevolute circle.

V In orderto provide cutting edges at opposite sides of the teeth, which are substantially identical and of the sharpness most desirable y,for efficient generating action,1the end faces the side face 3 and establishing the locus of points to form a cutting edge, Which'is of involute form andwhich lies in a plane at right angles (perpendicular) to the axis of the cutter.

The side faces 4 of the teeth` would normally intersect the end faces'of the teeth at an acute angle too sharp for the most effective generating action.` In order to form a cut- Y 7o thls invention, as herein referred to, by prO- v ting edge substantially identical with the locus of the points of the cutting edge formed by the intersecting involute helicoid surfaces 3 and 6, an external helieoid surface 7, involute to t-he same base cylinder as the side face 4, is generated along the edge of each tooth opposite that upon which theysurface 6 is generated. The'external involute helicoid surface 7 ,V is substantially normal to the involute helicoid surface 4, and intersects the same in a plane perpendicular to the axis of the cutter.

The helicoid surfaces G and 7. at their intersections with the helicoid side faces 3 and 4 of the teeth, form involutecutting edges 8 4 is generated. The helicoid surface 6, liowever, is an internal involute helicoid surface and must be generated with a grinding wheel of relatively small diameter, so disposed with respect to the surface 6 that the section through the grinding wheel, in the planeof lthe involute cutting edg'e being generated, is internally tangent to the involute during the generating movement.

In forming the cutter, the end face of the 7 cutter may beforiginally formed flat with its surface in al plane perpendicular to the axis of the cutter, in which case, after the ground back surfaces are formed on the end face,'flat portions 10 and 11 remain which were a part of the original flat surface.

While the external helieoid surface 7 may be generated with a grinding wheel of any desired diameter or by the engagement, of the flat face of a grinding wheel with the edge portion of the tooth, as in generating the involute helicoid side faces of the teeth, it will generally be found more convenient to l employ the saine grinding wheel for generator conical dlameter. i

ing the surface 7 as is employed for generating the surface 6.

In order to generate a true'involute down to the root line of the tooth at the cutting edge, it will benecessaryv to use a cylindrical grinding wheel of fairly small Figs. 5 and 6 show a cyindrical grinding wheel 12 in engagement with the helicoid surfaces 7 and 6. Ad s'indieated in Fig. 10 of 'the drawings, this grinding wheel is mounted Awith its axis A in a plane T tangent to the base cylinder BO of thecutterqand during' the generating action, there is a relative movement of the grinding wheel and cutter which is a combined rotative and translative movement, the cutter rotating about its axis in a direction indicated by the arrow R, and the grinding wheel having a relative linear movement in the tangent plane T in a direction indicated by arrow L at right angles to the axis of the cutter at a rate equal to the linear speed of a point on the b'ase cylinder of the cutter. The diameter of the cylindrical grinding wheel will be such that the elliptical section through the grinding wheel in the plane of the cutting edge being lgenerated which is perpendicular to the axis of the cutter will have a radius of curvature at its vertex not greater than the radius of curvature of the'involute at the root line of the tooth, so that during the entire generating action, the grinding wheel remains tangent to the involute curve of the cutting edge.

The maximum size for a cylindrical grinding wheel may be computed for any given cutter by the formula:

` p pi r d- 90 sin h where d is the diameter of the grinding wheel, E is the pressure angle, 1' the radius of the ase circle of the cutter and the angle of the heli'coid surface 6 to the plane of the cutting edge 8 measured on the base circle.

The grinding wheel-may be conical, if desired, and Figs. 7 and 8 show conical wheels 13 engaging the surfaces 6 and 7. When a grinding wheel of conical form is used, the maximum. diameter of the grinding wheel measured at the generating vertex of the ellipse in the plane of the cutting edge being generated may be computed by the formula:

p pi r sin (lL-2a) 90 sin (h-a) cosa where d is the diameter ofthe inding wheel,

lis the pressure angle, h is t e angle of the t: licoid surface 6 to the end face of the cutter measured at the base cylinderand a is the angle of taper' of the cone. Since the.

radius of curvature of an involute at any point is the length of the tan nt from that rer point lo the base circle, it will e obvious that a cylindrical or conical grinding wheel of a given diameter will correctl generate the internal involute outwardly fyrom the point on the involute where the radius of curvature of the involute equals the radius of curvature of the grinding wheel measured in the plane of the involute and that even though the grinding wheel be of a diameter somewhat greater than that re uired to correctly generate the involute to t e root line of the tooth,

the involute will becorrectly enerated to within a short distance from t eroot line and the error immediately adjacent the root line will be very slight. In some instances, the curvature at the root line may be so great that it may not be convenient to employ' a grinding wheel small enou h for theoretically correct generation to t e root line. In

such'cases, a. grinding wheel somewhat larger than the theoretically correct size may be emis a relatively small angle, the grinding wheel may be of larger diameter or may be in the form of a cone, with a taper opposite that shown in Figs. 7 and 8, in which case the section through the grindin wheel in the plane by providin vmi ven

of the cutting edge will e a hyperbola. In Fig. 9, a reversely tapered grinding wheel 14 is shown forgenerating. an internal helicoid surface disposed at a small angle to the l end face of the cutter. The cylindrical form of grinding wheel is considered preferable, since its elliptical section in the plane of the cutting edge has a radius of curvature at the vertex smaller than the correspondin section through a conical wheel such as s own in Figs. 7 and 8. The involute helicoid surfaces 6 and 7 may be generated with grinds ing wheels suchl as above described in a gear generating machine such as shown in my Patent No. 1,752,033 granted March 25, 1930,

o* on the grindingwheel head suitable means for mounting cylindrical or conical grinding wheels such as shown in Figs.

5 to 9. The grinding wheel will be mounted with its axis in a plane tangent tothe base cylinder of the cutter and in the operation of the machine, the work spindle carriage will be reciprocated into and out of engagementv with the grinding wheel with the rate-of linear movement of the carriage proportional to the speed of rotation of the cuttermeasured on the base cylinder. v

If the helicoid surfaces 6 and 7 are substantially normal tothe tooth:faces 3 and.4 at or near the root lines of theteeth, the angle between the tooth faces and helicoid surfaces at the ends of the teeth willl gradually deel crease toward the tips lof the teeth. The

difference in the angle, however, at the roots and tips of the teeth is slight and a slightly acute cutting edge is highly desirable.

It .will be apparent that the present inven tion provides a method of forming cutting edges at the endsV of helically disposed teeth which are true involutes .lying in planes perpendicular to the axis of the cutter, and such cutting edges will generate true involute tooth surfaces in a blank regardless of the angular position to the blank.

Furthermore, the present invention enables helical cutters to be successfully used which have teeth disposed athelix angles as great as 45.

What I claim is: 1. A gear sha d' cutter having peripheral teeth and an en face with helicoid 'surfaces Vofthe cutter with respect thereon, each surface intersecting a tooth face in a plane perpendicular to the axis of .the I cutter to form a cutting edge.

2.' A gear shaped cutter having teeth of involute form and an end face with 'helicoid surfaces thereon which are involute to the teeth of the cutter, each of said helicoid surfaces intersecting a toothA face to form a cut-v ting edge. V

A gear shaped cutter having an end face and teeth provided with helicoidside faces, 'said end face having helicoidsurfaces voppsitely inclined with respect to helicoid faces of the teeth, each surface intersecting a tooth faces involute with respect to the same base' -cylinder as the helicoid side faces of the teeth and intersecting said side faces to form involute cutting edges.

5. A gear shaped cutter having an end face and teeth provided with involute helicoid side faces, each tooth having an end face provided with involute helicoid surfaces intersecting the side faces at substantially rightangles to form involute cutting edges.

6. A gear shaped cutter having helicall disposed teeth of involute form, each toot Y same base Icylinder as the -side faces of the e having an end face provided with an internal involute helicoid surface intersecting a slde face of the tooth in a plane perpendicular to the axis of the cutter.

7 A gear shaped cutter having helically disposed teeth of involute form, each tooth having an end face provided with an internal involutehelicoid surface substantially nor'- mal to one of said side faces and intersecting the samezto provide an involutecutting edge. 8. A gear shaped cutter having helically disposed -teethof involute-form, each tooth having an end` face4 provided with two involute helicoid surfaces generated along the opposite edges of the tooth, one of said generated surfaces being internal-and one external.

9. A gear shaped cutter having helicallyv disposed teeth of involute form and an end face disposed substantially in a plane at right angles to the axis of the cutter, one side face of each'tooth intersecting the end face at an obtuse angle and the other at an acute angle, and involute helicoid surfaces enerated along the end edges of the teeth an substantially normal to the side faces to provide involute cutting edges.

10. A gear shaped cutter having helicall disposed teeth of involute form, each toot having an end face provided with an eX- ternal involute helicoid surface intersecting a side face of the tooth to form a cutting edge of involute form. f

11, The herein described method of forming cutting edgesat the ends of teeth of a gear shaped cutter which comprises generating on the end faces of the teeth helicoid surfaces each intersecting a side face of a tooth in a plane perpendicular to the axis of the cutter.

12.v The herein describedmethcd of forming cuttin edges at the ends of teeth of a gear shape cutter whose teeth have side faces of involute forin which comprises -generating on the end faces of the teeth helicoid surfaces which are involute to the same base cylinder as the side faces of the teeth and which intersect said side faces of the teeth to form involute cutting edges.v J v 13. The herein describedmethod of forming the cutting'edges at the ends of teeth of a gear shaped cutter whose teeth have side faces of involute helicoid form which comprises generatin along the `edges of said end faces of the teet helicoid surfaces involute to the saine base cylinder as the side faces of the teeth and each intersecting a sideface in plane perpendicular to theaxis of the cut- 14. The herein described method of forming the cutting edges at an end face of a gear shaped cutter whose teeth have side faces of involute form, which comprises generating on the end faces of the teeth heliccid surfaces which are involute to the same base cylinder as the side faces of theteeth and which 16. A gear shaped cutter havin helical teeth provided with involute side aces and end faces in a plane of revolution, said end faces of each tooth being provided with generated helical surfaces involute to the same base cylinder as the involute side faces .of the teeth, with one of such surfaces a righthand involute and another ail'efthand in volute, said surfas intersecting respectively an involute side face of the opposite hand.

17. A gear shaped cutter havin helical teeth provided withinvolute side acesand end faces in a plane of revolution, said end faces of each tooth being provided with generated helical surfaces involute to the same base cylinder as the involute side faces of the teeth, with one of the surfaces a righthand involute andanother a lefthand involute, said surfaces intersecting respectively an involute side .face of the opposite hand with one external and the other internal.

In testimony whereof I aiix in signature. l OLIVER G. SI ONS.

intersect said side faces of the teeth `to form `involute cutting edges by rotating a metal cutting element on an axis arran ed in a u cum.

plane tangentto the base cylinder o the cutter and incutting engagement withI the end .face of the-cutter rotating on its axis, and

imparting to the cutting element` a linearr movement in the-said tangential plane in a direction at right'angles to the axis of the cutter and at a rate equa-1 to the linearjspeed of a point on the base cylinder of the rotatl ing cutter. t A 15. The herein described method of forming the cutting edges on an end facel of a gear shapedcutter whose teeth have side faces of involute he1icoid form,'which comprises gen-A erating alon the edges of the end facesfof the teeth he icoid surfaces involutey to the same base cylinder as the side faces of the teeth and each. intersecting a side. face in a glane perpendicular to the axis of the cutter y rotating a cutting .element on an axis arranged in a plane tangent to the ,base cylinder of the cutter and in metal cutting engagement with the end face of the cutter rotating. y on its axis, and imparting to said cutting element and cutter a relative linear movement'in the 'said tangential plane and in a direction at right angles to the axis of the cutter at a rate equal to the linear speed of a point on the base cylinder of the rotating ixusY 

